Microstrip circulator wherein related microstrip patterns are disposed on opposing surfaces of dielectric substrate

ABSTRACT

This invention relates to a microstrip circulator used for steering electrical signals in predetermined directions along particular paths in a controlled manner. A particular embodiment of a microstrip circulator according to the present invention utilizes a non-ferrite dielectric substrate having metal film applied to both major surfaces of the substrate. The distributed electronic components of the circulator are formed in a circular configuration in the metal film on both major surfaces. A permanent magnet is spaced on one major surface directly over the circular configuration of electronic components and a ferrite disc is placed on the opposite major face directly opposite the magnet. A conductive groundplane is then applied to the outer surface and edges of the ferrite disc.

Elite ttes 1 Poirier [451 May 15, 1973 [75] Inventor: Arthur L. Poitier, Ottawa, Ontario,

Canada [73] Assignee: Her Majesty the Queen in right of Canada, as represented by the Minister of Defense, Canada [22] Filed: Dec. 7, 1971 [21] Appl. No.: 205,669

[52] U.S. Cl. ..333/1.1, 333/84 M [51] Int. Cl. ..H0lp 1/32 [58] Field of Search ..333/1.1, 24.1, 24.2,

[56] References Cited UNITED STATES PATENTS 3,467,918 9/1969 Dunn et al ..333/1.1

SUBSTRATE GROUNDPLANE 3,517,340 6/1970 Magalhaes ..333/1.l 3,521,195 7/1970 Bosma ..333/1.1 3,566,311 2/1971 Buck ..333/24.1 X 3,681,716 8/1972 Chiron et al. ..333/84 M Primary ExaminerPaul L. Gensler Attorney- R. S. Sciascia et al.

[57] ABSTRACT This invention relates to a microstrip circulator used for steering electrical signals in predetermined directions along particular paths in a controlled manner. A particular embodiment of a microstrip circulator according to the present invention utilizes a non-ferrite dielectric substrate having metal film applied to both major surfaces of the substrate. The distributed electronic components of the circulator are formed in a circular configuration in the metal film on both major surfaces. A permanent magnet is spaced on one major surface directly over the circular configuration of electronic components and a ferrite disc is placed on the opposite major face directly opposite the magnet. A conductive groundplane is then applied to the outer surface and edges of the ferrite disc.

7 Claims, 4 Drawing Figures INSULATOR 4 MICROSTRIP CIRCULATOR WHEREIN RELATED MICROSTRIP PATTERNS ARE DISPOSED N OPPOSING SURFACES OF DIELECTRIC SUBSTRATE STATEMENT OF GOVERNMENT INTEREST The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a microstrip circulator, used for steering electrical signals in predetermined directions along particular paths in a controlled manner. Such circulators are used, for example, in transmitterreceiver-antenna applications to maintain signal separation of the transmitted and received signals when using a common antenna.

2. Description of the Prior Art Existing designs used for incorporating circulators in microstrip circuits of the etched non-ferrite metallized dielectric substrate type are conventionally of one of the three following alternative types:

I. circulators fabricated as separate entities are connected to the microstrip circuit;

2. ferrite discs are mounted through holes machined in the substrate, the ferrite surfaces are metallized, and the circulator circuits are etched in conjunction with others in the system; or

3. the ferrite is placed on top of the substrate, the substrate under the ferrite is etched to provide a coupling means, the top and bottom surfaces of the ferrite are metallized and the circulator circuits etched on the surfaces of the ferrite. The third type of design is described, for example, in the IEEE transactions on Microwave Theory and Techniques Vol. M'IT-16 No. 12 pp 1060-1061 December, 1968.

Prefabricated circulators made in accordance with the first design type can be purchased commercially or fabricated by the user. Existing techniques for fabricating such circulators are relatively complicated and expensive, and require either vacuum or thick-film deposition equipment. The second design type requires accurate machining of the ferrite and the substrate. Ferrite is an extremely hard material, and is machined using diamond-tipped tools. A hole is machined in the substrate to accommodate a tight-fitting ferrite insert. The upper surfaces of the substrate and the ferrite insert, must be at the same level, with a very small gap at the junction, to allow bridging of the gap by the metal film that must be applied. Unless these two conditions are met, the metal film tends to break at the junction creating an open circuit in the circuit configuration. The third design technique, though less cumbersome than the previous two has inherent drawbacks: first, the ferrite is or should be machined to a fairly high degree of smoothness to ensure good circuit contact between the metallized substrate and its metallized bottom surface; and second, the ferrite must be metallized and etched on both surfaces, an expensive and time consuming process.

SUMMARY OF THE INVENTION In accordance with this invention there is provided a microstrip circulator of the type having an arrangement of distributed passive circuit elements connected to a plurality of ports, a ferrite body, a magnet, and a groundplane assembly; characterized in that the distributed passive circuit elements are formed out of opposite metallized surfaces of a non-ferrite dielectric substrate, the ferrite body is mounted adjacent one of said surfaces and the magnet is mounted on (but isulated from) the surface of the dielectric substrate opposite the one next to the ferrite.

A microstrip circulator according to the present invention eliminates problems of the type mentioned above encountered with previous designs for prefabricated circulators associated with microstrip circuits, namely: the necessity to precisely machine the substrate and the extremely hard ferrite material, the necessity of having a substrate-to-ferrite circuit path junction, the necessity to use prefabricated circulator entities separate from the microstrip substrate, and finally the necessity to etch the metal film applied to the ferrite.

OBJECTS OF THE INVENTION An object of the present invention is to provide a relatively inexpensive microstrip circulator, capable of being integrated into a substrate containing circuit components of the circulator and components of other circuits, and to avoid certain disadvantages of previous designs.

BRIEF DESCRIPTION OF THE DRAWINGS A particular embodiment of the invention is described below in detail in conjunction with the following figures of the drawings:

FIG. 1 shows a diagrammatic representation of any three-port circulator;

FIG. 2 shows an end view in partial section of a nonferrite metallized etched substrate incorporating the circulator components on, above and below the substrate, in accordance with the invention;

FIG. 3 is a top view of the substrate containing the circulator electronic components of FIG. 2, with the magnetic assembly removed;

FIG. 4 is a bottom view of the substrate containing the circulator electronic components of FIG. 2, with the circuit ground plane and the ferrite material removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Circulators are devices that make use of a phenomenon similar to that called Faraday rotation. The rotation results in the controlled steering of an input signal in a particular direction. Three port circulators are by far the most common. FIG. I is a diagrammatic representation of any three-port circulator either according to the invention or according to the prior art. When a signal is applied to port 1 it will emerge from port 2; if it is applied to port 2, it will emerge from port 3, and if applied to port 3, will emerge from port 1. In some circulators the direction of rotation is in the opposite sense. In other circulators, sense of rotation can be reversed from time to time at will.

The circulator configuration according to a preferred embodiment of the invention is shown in FIGS. 2, 3 and 4. With reference to FIG. 2, the circulator consists of a substrate 1, a slab or disc of ferrite 2, a magnet 3 and an insulating spacer 4. The magnet 3 is conveniently a permanent magnet, but could be an electromagnet if it were desired to be able to conveniently switch the direction of circulation (by changing the direction of the applied current).

Conductive metal layers 5 and 6 are bonded one on either side of the substrate 1. Circuit sub-assemblies 7 and 8 for the circulator of FIG. 2, are etched into the metal layers 5 and 6. The exposed surface of the ferrite 2 is metallized or coated with a conductive paint to form a conductive layer 9, functioning as part of the groundplane.

FIG. 3, the top view of the circulator, with the magnet 3 and spacer 4 removed, shows those electronic circuit sub-assemblies which are etched into the top metal layer 5. Quarter wave transformers 10 match the impedance of the circulator to a 50-ohm, input 16. Distributed inductive transmission line sections 11 connect the quarter wave transformer 10 to three capacitive pads 12. The capacitive pads 12 mate in one-toone correspondence with similar capacitive pads 13 on the lower surface of the substrate, creating a coupling capacitor through the substrate. The inductive sections of transmission lines 11 and the coupling capacitors components 12, 13 form series resonant circuits at the required center frequency.

FIG. 4, a bottom view of the three-port circulator, with the groundplane layer 9 and ferrite material 2 removed, shows those electronic components of the circulator etched into the metal layer 6 on the bottom surface of the substrate. Distributed inductive transmission line sections 14 join the capacitive pads 13 to a point 15 common to all three ports of the circulator. The capacitive pads 13 and the inductive sections 14 are conveniently formed by etching an originally continuous metal layer on the bottom of the substrate 1 so as to separate the circuit sub-assemblies 13 and 14 from the remaining metal layer 6. Circuit subassemblies 13 and 14 form a resonant pi network.

It should be understood that the electronic subassemblies labelled 7 and 8 in FIG. 2, represent in total or in part the various electronic components 10, 11, 12, 13 and 14 of FIGS. 3 and 4. The exact relationship between 7, 8 and 10, 11, 12, 13 and 14, is dependent on the particular position at which the sectional view of FIG. 2 is taken.

Since the permeability of the ferrite is a function of the applied magnetic biasing field, the inductance of the transmission line sections in the resonant pi network, and also the frequency of resonance of the network, can be controlled by varying the applied magnetic biasing field. The applied magnetic biasing field also determines the gyromagnetic characteristics of the ferrite. As a result, the center. frequency, the bandwidth, and the isolation of the circulator are functions of the circuit geometry, the type of ferrite used and the applied magnetic biasing field. (In the specific embodiment illustrated, the magnetic biasing field is created by the magnet 3).

An advantage of the present invention is its ease of fabrication. Non-ferrite substrates which are completely metallized on both sides, are commercially available. The circuit sub-assemblies 7 and 8, are etched into the metal film on both surfaces of the substrate 1, in the configuration required, as for example according to FIGS. 3 and 4. The magnet 3, and the spacer 4, are bonded together and attached to the top surface of the substrate above the circuit subassembly 7. The ferrite material is cut to an acceptable size, either disc shaped or slab shaped, and is bonded to the lower surface of the substrate 1, centrally located under circuit sub-assembly 8 of FIG. 2. To complete the fabrication of the microstrip circulator, a metal film or conductive paint 9, is applied to the edges and surface of the ferrite opposite the surface bonded to the substrate.

The magnet can be placed below the outer side of the conductive groundplane, centered on the circular circuit, as shown by 3' and 4' in FIG. 2. It is also possible to utilize two magnets one placed in the position as described in detail above, and the other magnet placed below the outer side of the conductive ground plane and centered over the circular circuit.

EXAMPLE A microstrip circulator according to the invention having a center operating frequency of 1750 MHZ was constructed using the following dimensions, materials and parameters:

Thickness of material (1) 0.020 Thickness of copper (5,6) 0.0013 (1.0 02) Diameter of circle to outer edges of pads (12) 0.5 Width of 50 ohm output lines (16) 0.020 Width of transformer lines (10) 0.026 Width of inductive lines (11) 0.014 Spacing between inductive lines (11) and pads (12) Width of inductive lines (15) 0.020

Width of gap between bottom pads (13) and bottom groundplane (6) Approx. 0.012

Length of transformers (10) 0.57

Ferrite 41rMs 400 Gauss Diameter of magnet 0.25

Length of magnet 0.1

Magnet material Alnico 9 What is claimed is:

l. A microstrip circulator of the type having an arrangement of distributed passive circuit elements connected to a plurality of ports, a ferrite body, a magnet, and a groundplane assembly; characterized in that the distributed passive circuit elements are formed on opposite surfaces of a non-ferrite dielectric substrate, the ferrite body is mounted adjacent one of said surfaces, the magnet is mounted opposite the ferrite and adjacent to but insulated from the other of said surfaces, and the groundplane assembly is formed by a metal layer disposed partly on said one surface of the substrate and partly on the surface of the ferrite body other than the surface thereof adjacent the substrate.

2. A microstrip circulator as defined in claim 1 including a non-conductive spacer separating said magnet from said other surface of said substrate.

3. A microstrip circulator as defined in claim 2, wherein said opposite surfaces are parallel.

4. A microstrip circulator as defined in claim 3, wherein said distributed passive circuit elements include at least one capacitive circuit element, for each of said ports, each of which capacitive circuit elements is formed as a pair of pads one on each of said opposite surfaces of the substrate, the substrate thereby constituting the dielectric material for the capacitive circuit elements.

5. A microstrip circular as defined in claim 4, wherein said distributed passive circuit elements are formed by etching the originally continuous metal layers on said opposite surfaces of said substrate.

6. A microstrip circulator comprising:

a non-ferrite dielectric substrate having at least one major face;

a ferrite body having at least one major face;

said ferrite bodymajor face being adjacent to the major face of the substrate, said substrate and ferrite body forming an assembly having two surfaces;

a passive circuit sub-assembly disposed between the substrate and the ferrite body;

a passive circuit sub-assembly disposed on one of said surfaces;

a metal layer constituting a groundplane disposed on the other said surface;

said other said surface of the assembly comprising at least partly a surface of the ferrite body; and,

at least one magnet mounted adjacent to but insulated from one of said surfaces.

7. A microstrip circulator comprising:

a non-ferrite dielectric substrate having first and sec- 0nd surfaces;

a first metal layer disposed on said first surface in a predetermined pattern;

a second metal layer disposed on said second surface and comprising:

a first part substantially covering all of the second surface except one area; and,

a second part electrically isolated from the first part disposed in said area in a pattern related to said predetermined pattern;

a ferrite body adjacent said second surface of the substrate and covering said second part of the second layer;

an electrically conductive coating on the surface of said ferrite body other than the surface thereof adjacent the substrate, the coating being in contact with the first part of the second metal layer;

a spacer of insulating material mounted adjacent said first metal layer; and,

a magnet mounted on said spacer.

UNITED STATES PATENT oEETcE CER'HECATE 0F ECTEQN Patent No. 3 ,733, 563 Dated May 8 1973 Inventor(s) ARTHUR L. POIRIER It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

On the cover sheet insert [30] Claims Priority Data Canada 107,627 Mar. 12, 1971 o Signed and sealed this 20th flay of November 1973.

(SEAL) Attest:

EDWARD M.FLE'I'CHER,JR. RENE Do TEGTMEYER Attesting Officer Acting Commissioner of Patents FORM po'wso (m'es) uscoMM-oc 60376-P69 9 US. GQVERNMENT PRINTING OFFICE Z ISQ 365-33, 

1. A microstrip circulator of the type having an arrangement of distributed passive circuit elements connected to a plurality of ports, a ferrite body, a magnet, and a groundplane assembly; characterized in that the distributed passive circuit elements are formed on opposite surfaces of a non-ferrite dielectric substrate, the ferrite body is mounted adjacent one of said surfaces, the magnet is mounted opposite the ferrite and adjacent to but insulated from the other of said surfaces, and the groundplane assembly is formed by a metal layer disposed partly on said one surface of the substrate and partly on the surface of the ferrite body other than the surface thereof adjacent the substrate.
 2. A microstrip circulator as defined in claim 1 including a non-conductive spacer separating said magnet from said other surface of said substrate.
 3. A microstrip circulator as defined in claim 2, wherein said opposite surfaces are parallel.
 4. A microstrip circulator as defined in claim 3, wherein said distributed passive circuit elements include at least one capacitive circuit element, for each of said ports, each of which capacitive circuit elements is formed as a pair of pads one on each of said opposite surfaces of the substrate, the substrate thereby constituting the dielectric material for the capacitive circuit elements.
 5. A microstrip circular as defined in claim 4, wherein said distributed passive circuit elements are formed by etching the originally continuous metal layers on said opposite surfaces of said substrate.
 6. A microstrip circulator comprising: a non-ferrite dielectric substrate having at least one major face; a ferrite body having at least one major face; said ferrite body- major face being adjacent to the major face of the substrate, said substrate and ferrite body forming an assembly having two surfaces; a passive circuit sub-assembly disposed between the substrate and the ferrite body; a passive circuit sub-assembly disposed on one of said surfaces; a metal layer constituting a groundplane disposed on the other said surface; said other said surface of the assembly comprising at least partly a surface of the ferrite body; and, at least one magnet mounted adjacent to but insulated from one of said surfaces.
 7. A microstrip circulator comprising: a non-ferrite dielectric substrate having first and second surfaces; a first metal layer disposed on said first surface in a predetermined pattern; a second metal layer disposed on said second surface and comprising: a first part substantially covering all of the second surface except one area; and, a second part electrically isolated from the first part disposed in said area in a pattern related to said predetermined pattern; a ferrite body adjacent said second surface of the substrate and covering said second part of the second layer; an electrically conductive coating on the surface of said ferrite body other than the surface thereof adjacent the substrate, the coating bEing in contact with the first part of the second metal layer; a spacer of insulating material mounted adjacent said first metal layer; and, a magnet mounted on said spacer. 